Tuesday, July 9, 2013

Investigation on how dissolving chemicals in water changes the freezing point of a solution.

Hypothesis

The higher amount of dissolving chemicals in water, the lower the freezing point of water.

Salt, also known as sodium chloride (CaCl2), lowers the freezing point of water. This process is called the freezing point depression. The freezing point depression can occur as long as there is a solution. Adding a solute, like salt, to a solvent, like water, lowers the freezing point of the solvent. However, the freezing point of the solvent varies in different conditions: the molality of the solution, the van't Hoff factor of the solute, and the molal freezing-point-depression constant of the solvent.

Molality, is defined as shown below:

Molality (moles/kg) = Moles (mol) of Solute/Kilograms (kg) of Solvent

Freezing point depression is a colligative property, a property that depends on the number of solute particles are in the solvent. The van't Hoff factor on the other hand, is how a molecule of a solute dissociates, or breaks apart, in the solvent. Covalent compounds, like sucrose (C12H22O11), do not dissociate in solution. These compounds have van't Hoff factors i = 1. Ionic compounds, like table salt (NaCl), dissociate when in solution. Table salt (NaCl) has a van't Hoff factor i = 2 because it dissociates into two ions in solution Na+ and Cl-. The third factor, the molal freezing-point-depression constant, Kf, is different for every solvent. It has units of (° C/m), and it tells indicates how much 1 mol of solute added to 1 kg of solvent will lower the solvent's freezing point. For pure water, Kf = 1.86° C/m. Combining these three factors—molality, m, van't Hoff factor, i, and molal freezing-point-depression constant, Kf—into an equation that predicts how much the freezing point of a solvent will decrease, ΔT, when a certain amount of solute is added.

Monday, July 8, 2013

Project Title 2: Investigation on the pH level of rainwaters collated around SST.

Hypothesis: The more polluted the air is in a location that the rainwater is located in SST, the lower the pH level.

Done by: Ain Nuha

Rainwater is water in form of droplets that are condensed from atmospheric water vapour and precipitated until it is heavy enough to fall because of gravity. Rain is important to the water cycle as it deposits the most fresh water on Earth. Also, rain provides a lot of suitable condition for the eco-system. Rainwater varies in terms of the pH level, mostly due to its origin. The places of where rainwater is from affects the pH level of it. For an example, rain that is collected from the Atlantic Ocean has a pH level of 5.0 to 5.6. (Whereas, rain that is collected across the continental from the west has a pH level of 3.8 to 4.8. With that, we want to know on how the location of where the rainwater is collected affects the pH level and what are the factors that would change the pH level of the rainwater collected in SST.

Project Title 3: Investigation on how dissolving chemicals in water changes the freezing point of a solution.

Hypothesis: The higher amount of dissolving chemicals in water, the lower the freezing point of water.

Done by: Liew Yee Theng

Through some research, salt, otherwise known as sodium chloride (CaCl2), lowers the freezing point of water. This process is known as freezing point depression and it can occur as long as we have a solution. Adding a solute, like salt, to a solvent, like water, lowers the freezing point of the solvent. The answer to how much the freezing point of the solution depends on three things: the molality of the solution, the van't Hoff factor of the solute, and the molal freezing-point-depression constant of the solvent.

Freezing point depression is a colligative property, a property that depend on how many solute particles are in the solvent, not the kind of solute particles. Molality, m, is one piece of this "how many solute particles are present?" question. The van't Hoff factor is the second part of the "how many solute particles are present?" question.

The van't Hoff factor, i, deals with how a molecule of solute dissociates, or breaks apart, in the solvent. Covalent compounds, like sucrose (C12H22O11), do not dissociate in solution. These compounds have van't Hoff factors i = 1. Ionic compounds, like table salt (NaCl), dissociate when in solution. Table salt (NaCl) has a van't Hoff factor i = 2 because it dissociates into two ions in solution, Na+ and Cl-.

The third factor, the molal freezing-point-depression constant, Kf, is different for every solvent. It has units of (° C/m), and it tells us how much 1 mol of solute added to 1 kg of solvent will lower the solvent's freezing point. For pure water, Kf = 1.86° C/m.

Combining these three factors—molality, m, van't Hoff factor, i, and molal freezing-point-depression constant, Kf—into an equation that predicts how much the freezing point of a solvent will decrease, ΔT, when a certain amount of solute is added. Equation 2, below, is the freezing point depression equation:

Kf is the molal feezing-point-depression constant in degrees Celsius per molal (° C/m)

m is the molality of the solution in moles per kilogram (mol/kg)

i is the van't Hoff factor of the solute, which does not have units

In order to find out the new freezing point of a solution, Tn, subtract the change in temperature, ΔT, from the original freezing point, Tf, as shown in Equation 3, the solution freezing point equation:

Monday, July 1, 2013

Scientific Methods are techniques or procedures that one would do in order to attain a certain result or a new knowledge using methods based on the principles of science. Scientific methods consists of making up a hypothesis by asking a relevant question, and to conduct an experiment to find out a conclusion as to the question asked in the first place. Scientific methods may vary.